Last menstrual period

Last Menstrual Period (LMP) is a term used in Obstetrics and Gynecology to denote the start of a woman's most recent menstrual cycle. It is a crucial date in the calculation of a pregnancy's due date, often referred to as the Estimated Date of Delivery (EDD).

Definition

The Last Menstrual Period is the first day of the last menstrual bleeding. It is used as a reference point in the calculation of the gestational age of a pregnancy. The gestational age is calculated from the LMP, assuming a regular menstrual cycle of 28 days with ovulation occurring on the 14th day.

Clinical Significance

The LMP is used in obstetric history taking and is crucial in the calculation of the Estimated Date of Delivery (EDD). The EDD is calculated by adding 280 days (or 40 weeks) to the LMP in a woman with a regular menstrual cycle. This method, known as Naegele's rule, assumes a 28-day cycle with ovulation occurring on the 14th day.

In cases where the menstrual cycle is irregular, or the LMP is not known, other methods may be used to estimate the gestational age and EDD. These include ultrasound scanning and physical examination.

Limitations

The use of LMP to calculate the EDD has limitations. It assumes a regular menstrual cycle, which is not the case for all women. It also assumes that conception occurs on the 14th day of the cycle, which may not always be the case. Furthermore, it relies on accurate recall of the LMP by the woman, which may not always be reliable.

See Also

• Menstrual Cycle
• Obstetric history
• Gestational age
• Estimated date of delivery

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